The invention relates to a system for drying waste, mare particularly to a system for drying a wide range of sludge and other materials which vary in moisture content.
Environmental concerns have motivated a search for waste disposal systems capable of disposing of waste materials in accordance with the applicable regulating standards. The most widely used of these disposal means comprises incinerating the waste materials. It has ben discovered that incineration of such waste is most efficient if the material is preconditioned through drying before it is incinerated. However, conventional waste disposal systems incinerate waste without drying or with only minimal drying. Those systems that do dry waste materials typically include a dryer that removes a portion of the liquids from the waste materials. For example, U.S. Pat. No. 3,716,002 (Porter et al.) discloses a solid waste disposal system in which high-moisture content wastes are conveyed through a dryer where they are mixed with hot gasses before they are incinerated. But in order to avoid pre-mature combustion of the materials, the temperature of the gasses are not high enough to completely dry the wastes, requiring the recirculation of partially dried waste into the inlet of the dryer to premix with wet incoming waste such that the mixture has a reduced moisture content per unit weight of dryer throughput. This system thus is inefficient in that only a fraction of the material that is dried is actually passed on to the burner. Furthermore, there are no means in the dryer to ensure that the wastes are uniformly dried before they are conveyed to the burner.
Other conventional systems which dry waste materials are relatively inefficient and are incapable of accommodating a wide range of waste materials. To handle sludge materials having a high moisture content, for example, conventional systems must consume an excessive amount of fuel to uniformly dry high-moisture materials to a level necessary for complete combustion, resulting in an extremely inefficient drying operation. In addition, these systems are inflexible because they must be individually designed to dispose of a narrow range of waste materials. They are further limited in their treatment of a particular material, e.g. sludge, in that they burn prematurely (over-condition) materials of a relatively low moisture level and fail to adequately dry materials of a relatively high moisture level (under-conditioning).